Catalytic hydrogenation is one of the key processes for manufacturing pharmaceuticals, vitamins and fine chemicals. The performance of the hydrogenation process and product distribution is influenced by the catalyst activity and selectivity, which in turn is strongly dependent on the metal particles morphology and their size. The main problem in studying the size effects in catalytic hydrogenations is that the particle size should be varied keeping all other parameters constant. Moreover, the interaction of chemical kinetics with mass & heat transfer should be avoided. This can be achieved by the appropriate design of the reactor used.

One approach to overcome these problems is the use of monodispersed nanoparticles of different size, but prepared in the same manner. Herein, we report a new method of the preparation of Pd-cluster with a narrow size distribution via reversed micro-emulsion of water in isooctane, followed by nanoparticles extraction from microemulsion and their redispersion directly in the hydrogenating substrate. Size of Pd-clusters is mainly governed by a water-to-surfactant ratio and was between 6 and 13 nm. It is important to note that no studies on the size-effect in hydrogenation of acetylenic alcohols were performed up-to-now for the particle size above 7.5 nm. Usually, it is considered that the structure-sensitive reactions do not reveal size dependence above 5 nm owing to the small contribution of the atoms with low coordination numbers on the nanoparticle surface in this range.

As a test reaction, hydrogenation of 2-methyl-3-butyn-2-ol (MBY) to 2-methyl-3-buten-2-ol (MBE) was chosen. The product MBE is an important intermediate in the synthesis of vitamins A and E and perfumes. The reaction is also interesting for basic catalysis because of several by-products formation. This allows elucidating an influence of cluster size on product distribution besides controlling the selectivity towards the target MBE. Kinetics of MBY hydrogenation was studied and simulated based on Langmuir-Hinschelwood model. The Pd-clusters were characterized by high-resolution transmission electron microscopy, an energy-dispersive X-ray (EDX) and XRD methods.

In addition to the use of Pd-cluster per se, they were deposited on active carbon fibres in the form of woven fabrics. This allows understanding an influence of the support on the catalytic performance of Pd°-nanoparticles and to suggest an alternative reactor design based on structured catalytic bed. The results will be presented in detail.